Air conditioning units of the aforedescribed type are referred to as room air conditioners. The reference to human applications of such air conditioning units is intended to indicate that the air conditioner is primarily for rooms occupied by people including offices, domiciles, theaters, commercial establishments, hospitals, schools and other institutions.
The reference to air conditioning is here intended to cover complete conditioning systems as well as partial conditioning systems. Complete conditioning systems are those which can effect all four thermodynamic air treatment functions, namely, heating, cooling, moisturization or humidification and dehumidification to appropriate levels or with appropriate controls. Such units thus contain control devices for all four of the thermodynamic conditions.
Partial conditioning systems are those which provide reduced functions, for example, only cooling. The control systems are correspondingly reduced in such arrangements.
Conditioning systems of the described type and for the described purposes are well known for domiciles. Their construction and configurations have been designed to satisfy air conditioning technology requirements for such domiciles. Nevertheless they can be improved upon.
In the past, for example, conditioned room air was not completely free from suspended matter and molecular impurities that could collectively be referred to as contaminants. The reference to suspended matter is intended to cover both inorganic and organic particulates, including viruses, bacteria, fungi or molds. In addition, the blower generated considerable noise, usually in a frequency range of 125 to 250 Hz. The sound level at the outlet of the blower increased with blower power and decreased along the duct to the air outlet. Nonetheless there was a high sound level at the outlet of the blower with a high sound level in the space to which the treated air was admitted.
With conventional air conditioning systems of the type over which the present invention is an improvement (see, for example, Recknagel, Sprenger, Homann "Taschenbuch der Heizungs- und Klimatechnik", R. Oldenburg Verlag Munchen und Wien 1987, Pg, 900, FIG. 329-2), it is known to equip a central air conditioning unit with a filter device. This is provided upstream of the units which effect the conditioning of the air and filters the fresh air entering the central unit and/or the recirculated air delivered thereto. To reduce the noise below a detrimental level and to suppress noise generally, it is known to form the feed duct of the treated room air so that it is of a sound-damping nature and/or to combine this duct with sound-damping features (see Recknagel, Sprenger, Honmann, loc. cit. pg. 1073 to 1076).
It is also known, in this connection, to provide sound-blocking structures for such systems. Sound-blocking refers to the interference with the spreading or transmission of sound by interposing sound reflecting barriers or materials. A measurement for the degree of sound blocking is the sound blocking coefficient or the degree of sound transmission (ratio of transmitted sound to generated sound). In order to generate a maximum possible sound reflection, a medium must be provided in the sound path whose sound damping impedence differs from that of the sound transmission medium, i.e. the treated room air, to the greatest possible extent. For example, a high density, high weight solid mass can serve as an effective sound blocking medium as interposed along a sound path because of its much greater sound block impedence than the impedence of the propagation medium, namely, room air.
For air transmitted sound, therefore, sound blocking requires hard and heavy materials in the form of walls for high sound frequencies while for lower frequencies the use of walls of relatively soft bendable materials or body vibration materials are used.
For sound-damping, i.e. the reduction of sound transmission or the attenuation of sound, sound absorbing media or devices are used. A measure of sound damping is the degree of sound adsorption, i.e. the proportion of the sound impinging upon a surface which is transmitted through it. Sound-damping is a characteristic of materials which are particularly suitable for blocking sound transmission and in general some of these materials will also give rise to a noticeable sound-damping. Sound-damping materials seldom block all sound, although they will give rise to a significant attenuation, i.e. should have a sound adsorption of at least 10% and usually much more. Sound-damping materials are usually materials which convert sound to thermal energy by internal friction. The field is aware of many sound-damping and sound-blocking materials and the conditions under which both may be used or provided to achieve either sound-damping or sound-attenuation or both.
With the previously described known air conditioning systems, providing filter units upstream of the central unit, even with said ducts which have sound-damping or sound-blocking devices associated therewith, the filter unit and the sound-damping or sound-blocking unit operate individually and additively as far as energy losses are concerned. As a consequence, the blower capacity must be increased and this results in ah increased noise level at the blower outlet.